[Gmsh] Double surfaces after STEP import

[Zenker, Dr. Matthias]

Hi Mark,

in the meantime, I have discovered two (at least partial) solutions on the Elmer side:

1) At mesh import, Elmer can merge nodes which are near to each other. I order to use this, both surfaces have to be meshed with the same characteristic length. The threshold distance for node merging is a parameter you can set. Drawback: If there are several interfaces with different mesh widths, this method might fail.
2) By "misusung" periodic boundary conditions, Elmer can be told that certain variables are continuous at the interface even if the meshes do not match. I did not use this yet, and it seems that care has to be taken in some cases, e.g. with direct solvers.

Other FEM programs might have similar possibilities.

But still, a proper cleanup of double interfaces on gmsh side would be the best solution since it tackles the cause of the problem directly.

So if there is such a solution someday, I would still be most interested (and I might not be the only one).

Best regards,

Matthias

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ERBE Elektromedizin GmbH
Dr.rer.nat. Matthias Zenker
Dipl. Phys.
Grundlagenentwicklung / Fundamental Development
Waldhoernlestrasse 17
D-72072 Tuebingen
Phone + 49 (0) 7071 - 755 226
Fax + 49 (0) 7071 - 755 5226
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-----Ursprüngliche Nachricht-----
Von: Mark van Doesburg [mailto:mark.van.doesburg at technolution.nl] 
Gesendet: Montag, 13. September 2010 09:58
An: Zenker, Dr. Matthias; gmsh at geuz.org
Betreff: Re: [Gmsh] Double surfaces after STEP import

Hello Matthias,

I worked on that code and consider it a complete faillure. In many cases the OpenCASCADE algorithms would not find the intersections. The initial version was quite simple but at some point I started to stack one workaround on top of the other.

Currently I do not have the time to work on another method, but some algorithms available in CGAL look promising. But in that case I would probably use BRL-CAD to generate the geometry, and importing STEP into BRL-CAD might be sub-optimal.

regards,

Mark

"Zenker, Dr. Matthias" <Matthias.Zenker at erbe-med.de> wrote:

	Hi,

	I have not done FEM calculations for some time (a year or so). The last
	time I did them (using gmsh and Elmer), I had the problem that in
	geometries imported as STEP files (generated by Solidworks), adjacent
	bodies have their own external surface, resulting in double surfaces at
	the interfaces. When I use the mesh generated by gmsh in a FEM
	calculation (I use Elmer), I get no thermal and electrical connection
	because the body meshes are not connected at the interface. There have
	been attempts to clean up double surfaces in gmsh, but I don't know if
	they have come to a success. Could someone of the developpers update me
	on this point?

	Thank you!

	Matthias 

	----------------------------------------------------------------
	ERBE Elektromedizin GmbH
	Dr.rer.nat. Matthias Zenker
	Dipl. Phys.
	Grundlagenentwicklung / Fundamental Development
	Waldhoernlestrasse 17
	D-72072 Tuebingen
	Phone + 49 (0) 7071 - 755 226
	Fax + 49 (0) 7071 - 755 5226
	E-Mail: <mailto:Matthias.Zenker at erbe-med.de>
	URL: http://www.ERBE-med.de
	----------------------------------------------------------------


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	ERBE Elektromedizin GmbH
	Firmensitz: 72072 Tuebingen
	Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
	Registergericht: Stuttgart HRB 380137


_____________________________________________________________________
ERBE Elektromedizin GmbH
Firmensitz: 72072 Tuebingen
Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
Registergericht: Stuttgart HRB 380137